1. Field of the Invention
The present invention relates to two-dimensional noise shaping filter circuit for performing noise shaping operations for a video signal.
2. Background of the Invention
As an example of a noise shaping circuit, the circuit shown in FIG. 19 has been used for shaping noises in a signal to be processed. The noise shaping circuit shown in the drawing includes an adder 101, a quantizer 102, another adder 103 and a transfer function unit 104. The signal to be processed is received at the quantizer 102 and quantized there. Quantizing distortion caused by the quantizing process is fed back to the input stage through the transfer function unit 104. An output signal is obtained by the quantizing process while minimizing the quantizing distortion. The adder 101 adds the signal to be processed with the signal fed back from the transfer function unit 104. The adder 101 then sends the signal obtained by this process to both the quantizer 102 and another adder 103. The quantizer 102 receives the output of the adder 101 and quantizes it by a predetermined bit number. The output signal as obtained by this quantizing process is supplied to the another adder 103. The adder 103 subtracts the output signal of the adder 101 from the output of the quantizer 102 so as to generate a signal representative of the quantizing error during the quantizing process at the quantizer 102. This quantizing error signal is supplied to the transfer function unit 104. When receiving the quantizing error signal from the adder 103, the transfer function unit 104 works as a filter with a predetermined filtering characteristics. It sends the signal obtained by this filtering process back to the adder 101 as a feedback signal. Whenever a signal to be processed is supplied, this conventional noise shaping circuit receives the signal to be quantized and sends the quantizing distortion generated by the quantizing process back to input stage through the transfer function unit 104 as feedback. By minimizing the quantizing distortion, the noise shaping circuit generates an output having a characteristic as described below.